Temperature gauge problems 4510

Hey everyone. I have a 2004 4510 FWD that today started showing the temp needle all the way into the red. The water pump is ok. The water in the rediator is warm, but not scalding like the gauge would indicate. Called my local dealer and they assumed it to be the sensor located on the water pump. They said they had one in stock. I purchased it ($81 bucks) and replaced it. Started the tractor up and all looked normal...til I proceeded to drive off and noticed the gauge was all the way over to HOT again. I put my old one back in and continued to cut grass, when I noticed the gauge was showing normal again. While I was looking at it, it went back to HOT again instantly. Obviously some electrical problem. Now they are't sure if it's something in the wiring or the gauge itself. What are my options here, and what could be the problem? Thanks.